The present invention relates to the field of triggering synchronized actions in downhole environments, such as along a drill string used in oil and gas exploration, or along the casings used in production wells and other equipment used in oil and gas production.
Triggering a seismic source and simultaneously collecting data has been expressed for more than half a century. The precise relationship between the time the seismic source triggers and the time the seismic receivers collect data may be useful in determining subterranean formations and thereby improve oil, gas, and geothermal well exploration and production. For example, to determine the subterranean formations surrounding a well bore, it may be beneficial to record seismic data synchronously with the triggering of a seismic source. Also, it may be useful to trigger multiple seismic sources synchronously. Several methods and systems to take such measurements, and correlate the times of triggering two actions are known in the art. In the downhole environment, systems and methods have been developed that have direct communication by wire or through fluid to the downhole device, and trigger a downhole device according to instructions received via these methods.
One example of such systems is described in U.S. Pat. No. 6,624,759 to Tubel , et al., which discloses a communication system that enables communication from a surface location to a downhole location where instructions communicated are executed. The system employs accelerometers to sense vibrations traveling within the annulus fluid or the tubing string. The accelerators provide signals representative of the vibration generated at the surface of the well to a microcontroller. The microcontroller is programmed to energize a nichrome element to actuate the downhole tool in response to a user-defined vibration sequence. The vibration sequence includes a defined number of vibration cycles. Each cycle includes alternating periods of vibration and no vibrations with each period lasting for a defined length of time. The user may program the parameters of the sequence and arm the vibration receiving unit on site through a handheld terminal that interfaces with the microcontroller.
Several systems for actuating or triggering downhole tools are described in U.S. Pat. Nos. 6,349,766; 5,558,153; and 4,471,435 and describe a variety of non-electrical methods to trigger a downhole tool. These methods include placing a chemical sensor downhole and introducing a chemical slug into fluids being pumped downhole, or using a burst of neutrons downhole to trigger a downhole tool.
U.S. Pat. No. 6,386,108 to Brooks, et al. discloses the initiation of one or more explosive devices. In response to activation of a trigger signal down the electrical cable, a switch coupling the energy source and an initiator is closed to couple the energy source to the initiator.
A system that may be used to trigger downhole actions is disclosed in U.S. Pat. No. 6,670,880 to Hall, et al. which discloses a system for transmitting data through a string of downhole components. In one aspect, the system includes first and second magnetically conductive, electrically insulating elements at both ends of the component. Each element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. An electrically conducting coil is located in each trough. An electrical conductor connects the coils in each component. In operation, a varying current applied to a first coil in one component generates a varying magnetic field in the first magnetically conductive, electrically insulating element, which varying magnetic field is conducted to and thereby produces a varying magnetic field in the second magnetically conductive, electrically insulating element of a connected component, which magnetic field thereby generates a varying electrical current in the second coil in the connected component.